The present invention relates to a fuel supply apparatus for low boiling point fuel vaporized at normal temperatures and under atmospheric pressures, and specifically to preventing vaporization and leakage of the fuel.
From the point of view regarding to the terrestrial environment problems typified by global warming and the energy problems, low carbon fuels such as natural gas (CNG, LNG), liquefied petroleum gas (LPG) and dimethyl ether (DME) are being introduced for the engines such as automobile internal combustion engine. As the number of carbon atoms in the individual fuel molecule is less than that of the gasoline and the petroleum, and their heat release value per a single carbon atom is higher than that of the gasoline and the petroleum, the number of carbon atoms for an identical heat release value becomes reduced in those fuels. This means that the amount of emitted gaseous CO2 from the engine can be reduced, which leads advantageously to preventing the global warming and to the energy saving. An application of DME is proved to be valid for an alternative fuel for the diesel engines because it is proved that there is no soot generated. As those low carbon fuels have low boiling point and stay in a gaseous phase at normal temperatures and under an atmospheric pressure. For example, in case of applying those fuels into diesel engines, it is required to maintain its liquid phase by pressurizing or cooling the fuel properly and to inject the fuel into the combustion chamber by using a high pressure pump. In this operation, there are such problems as defect in the fuel feed operation and fuel leakage outside the fuel supply system due to the fuel vaporization in the fuel pipe extended from the fuel tank because the fuel has a low boiling point. As for the technologies solving those problems, there disclosed a technology found in Japanese Patent Laid-Open Number 2001-115916 in which the feed pressure in the feed pump installed in the fuel tank is controlled in responsive to the map prepared based on the DME vapor pressure chart and the detected value of the fuel pressure.
There still remain such problems in the prior art as described below.
As the vapor pressure chart of the fuel is determined uniquely by the fuel temperature, the feed pressure of the fuel pump is dominated by the fuel temperature at the sensing point of the temperature sensor. This means that this technology can not solve the fuel vaporization or leakage in case that there exists a local heat spot in the fuel pipe.